Process for the preparation of copy sheet



United States Patent 3,486,936 PROCESS FOR THE PREPARATION OF COPY SHEET David R. Cahill, Wilbraham, Mass., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Feb. 21, 1967, Ser. No. 617,485 Int. Cl. H01b 1/06; B44d 5/00 US. Cl. 117-224 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a sheet material with electrically conducting properties for use in photoconductive, electroconductive and other related copying systems wherein the sheet material has dispersed therein a watersoluble conductive substance comprising from 25 to 100 weight percent of sulfonated polystyrene and salts thereof and from zero to 75 weight percent of a salt of sulfuric acid and derivatives thereof such as sulfamic acid, wherein in each case the weight percent is based on the total weight of the water-soluble conductive substance.

This sheet material is then treated further with the conventional photosensitive agents and adjuncts such as film forming resins, zinc oxide, binders, pigmented resins, etc.

This invention relates to a sheet material for use in photoconductive, electroconductive and other related reproducing, recording or printing means, wherein the sheet material is prepared by treatment with a water-soluble conductive substance.

In the known photoconductive, electroconductive and other related reproducing, recording and printing processes it is necessary to have a sheet material with a surface which will accept an electrostatic charge and hold it for at least several minutes in the dark. Exposure of the charged surface to actini c radiation makes the exposed areas conductive and causes dissipation of the charge from those areas. In these reproducing, recording and/ or printing processes the entire photoconductive surface, while protected from light, is given an electrostatic charge as by friction or more commonly by exposure to an electrical corona discharge. The charged surface is then exposed to a pattern of actinic-radiation as through a transparency or by reflection from a patterned surface, which discharges the exposed areas but leaves the unexposed areas still charged in the form of a latent image. The exposed surface is then brought into contact with a colored resinous powder which preferably has a charge opposite to that of the still charged areas of the surface. The powder clings to the charged areas of the latent image but does not adhere to, or is easily removed from, the discharged or exposed areas. Thus a visible image is formed on the charged area which visible image may be transferred to another surface or it may be heated and fused in place on the areas of the original latent image.

The sensitization of the surface of the sheet material by the application of a blanket, positive or negative electrostatic charge to its exposed surface. During the copying process the sheet is grounded by placing the sheet material on a grounded electrical conductor. For this reason it is necessary for the sheet to be an electrical conductor to ground the lower surface of its coating to the electrically grounded conduct-or on which it rests. In the case of 3,486,936 Patented Dec. 30, 1969 ICC a sheet having a minimal electrical conductivity, it is necessary for the sheet to be in close and uniform contact with the electrically conductive surface on which it rests to secure a uniform dissipation of electricity from all parts of the sheet. In the case of a sheet having good electrical conductivity, such close contact is unnecessary, although the sheet must be electrically grounded at one or more points.

This latter type sheet material which is characterized by having good electrical conductivity is especially preferred in the art because it is more conducive to speed of copying and clarity of copy than those sheets having poor conductivity. This requirement of good electrical conductivity is a source of major difficulty in securing uniformly satisfactory performance with photoelectric or photoconductive reproduction papers under different climatic conditions of humidity and temperature as Well as the variations encountered from one type machine to another.

Much effort has been expended trying to develop a conductive sheet material which will exhibit a high degree of electroconductivity under varying environmental conditions of temperature, relative humidity, sheet moisture, etc., as well as under the varying operating conditions which are encountered from one copying process and/or machine to the next.

Various means have been described in the patent art for increasing the conductivity of sheet material which is used in photoelectric or electroconductive copying processes. Illustrative of these are such US. patents as 3,011,918; 3,113,022; 3,116,147; 3,153,591 and 3,216,853. These patents teach copying paper which has been treated with such compounds as vinylbenzyl quaternary ammonium compounds, aryl diazonium salts, hygroscopic inorganic salts and 4-amino-naphthalimide.

The foregoing approaches, while representing valuable contributions to the art, have certain drawbacks which detract from their overall usefulness. These drawbacks include loss of conductivity under conditions of varying humidity, poor aging properties, poor hold out against solvent based resins used to coat the sheet material, migration of the conductive material in the sheet, difficulty of preparation, undesirable odors, etc.

Furthermore, the use of impregnating agents in paper causes an undesirable decrease of opacity and an increase in translucency or transparency in the paper. In order to overcome this detrimental effect, the impregnating agent must be compounded with various types of clay which would extend and opacify the paper.

Many of the currently available conductive materials cited in the prior art are incompatible or only slightly compatible with fillers, extenders, opacifiers and fil-m forming materials such as starch, resins, etc. which are used in the paper making trade. This problem severely limits the use of these conductive materials in electroconductive copying paper.

The use of hygroscopic salts alone as the conductive material in electroconductive copying paper is not entirely satisfactory as changes in the amounts used and the ambient relative humidity will result in changes in the nature of the paper. The hygroscopic nature of the salts may cause water pick up to the point that the sheet feels raggy,

, that is, limp and damp.

material for treating sheet material used in electroconductive and photoconductive reproducing, copying and printing processes, which material will be compatible with the other paper-making additives and will maintain a high electroconductivity under widely varying conditions of temperature and humidity.

A further need exists for an easy to prepare, water soluble, electroconductive material which can be used to treat sheet material used in electroconductive and photoconductive-type reproducing, copying and printing processes.

It is an object of this invention to provide Water soluble conductive material for treating sheet material used in electroconductive and photoconductive reproducing, copying and printing processes, which material will maintain a high electroconductivity under varying conditions of temperature and humidity.

It is a further object of this invention to provide a low cost, easy to prepare, water soluble, conductive material which can be used to treat sheet material used in electroconductive and photoconductive reproducing, copying and printing processes.

It is a further object of this invention to provide a process for the treating of sheet material used in electroconductive and photoconductive reproducing, copying and printing processes.

These and other objects are obtained by electroconductive sheet material comprising a fiber base having dispersed therein from 0.5 to 15.0 lbs. per 3000 square feet of fiber base of a water soluble conductive material comprising from 25 to 100 weight percent of sulfonated polystyrene and salts thereof and from to 75 Weight percent of a salt of sulfuric acid and its derivatives wherein in each case the weight percent is based on the total weight of water soluble conductive material and wherein the cation in the respective salts is selected from the group consisting of ammonium, alkali metals and amines.

The following examples are set forth in illustration of this invention and should not be construed as limitations thereof. Unless otherwise indicated all parts and percentages are given in terms of parts by weight.

Wherever practical, the term paper will be used to include sheet or web material which may be treated with the water soluble conductive materials of this invention. The term paper is meant to include cellulosic fiber and synthetic fiber sheet material upon which printing, photos and other images are recorded. The term ammonium is meant to include substituted ammonium or amines such as ethanol amine, morpholine, picoline, etc. which are generally recognized as derivatives or substituted ammonium.

The conductivity tests described below are carried out according to the procedure of D. G. Brubaker, Testing of Electrophotographic Papers and Coating Formulations, TAPPI, vol. 46, No. 5, May 1963, pages 312-316. Unless otherwise indicated any treated or untreated paper stock used is conditioned for five days at constant temperature and humidity prior to testing for electroconductivity. For the sake of uniformity and ease of comparison unless otherwise indicated the paper stock used is Riegel EC3 SXE base stock. However, it should be noted that this invention is applicable to those papers generally used in the photoelectric or electroconductive reproducing or copying systems and should not be construed as being limited to any particular base stock.

EXAMPLE 1 This example is set forth as a control to illustrate the poor conductivity of paper stock that has not been treated in accordance with the teaching of this invention.

Control stock The following Examples 2-6 are set forth to illustrate the significant increase in conductivity of paper stock that has been treated with a solution of ammonium salt of sulfonated polystyrene in accordance with the teachings of this invention. A 15% solution of ammonium salt of sulfonated polystyrene was applied to the paper stock using wound wire rods of varying size. The conductivity values shown are given for various applied weights at two different relative humidities. The conductivity results of Examples 2-6 are tabulated in Table I.

TABLE I.OONDUCTIVITY RESULTS FOR THE AMMO- A comparison of Examples 2-6, which are listed in Table I, with the control sample of Example 1 will demonstrate the significant increase in the conductivity of paper that has been treated with the ammonium salt of sulfonated polystyrene. Note that even at relative humidities as low as 12% that a significant and unexpected increase in conductivity is achieved when using the sulfonated polystyrene salts of this invention. These results are even more surprising when one considers that at 12% relative humidity there is little moisture available in the paper sheet to enhance the conductivity of this polymeric material.

EXAMPLE 7 This example is set forth to illustrate the conductivity of paper that has been treated with a salt of a derivative of sulfuric acid. Paper stock is treated with a 30% aqueous solution of ammonium sulfamate to give a dry application weight of 2.6 lbs/3000 sq. ft. Paper treated in this manner was found to have the following conductivities at the relative humidities indicated:

Percent R.O. Megohms/ Square 41 22 14 19,000

Note that at the lower humidity levels that ammonium salt of sulfonated polystyrene (Examples 2-6) shows about 10 times more conductivity than the ammonium sulfamate of Example 7. Note further that paper treated with either material has significantly higher conductivity than that of the control stock of Example 1.

The sulfonated polystyrene material of Examples 2 to 6 is to be preferred over the salts of sulfuric acid and its derivatives because the polymeric material has little or no tendency to migrate within the paper sheet and is less senstive to conditions of low humidity as is indicated by the respective values set forth above. Furthermore, at conditions of high humidity, e.g., 70 to RH, the hyroscopicity of these salts when used alone at levels to insure adequate performance at lower humidity levels, causes a limpness or raggy feeling in the paper stock.

Surprisingly, it has been discovered that a mixture of sulfonated polystyrene and the salts thereof and the salts of sulfuric acid and its derivatives may be used to great advantage as the conductive material in photoelectric or electroconductive paper. These mixtures show electroconductivity that is better than either material used alone at any given weight. Furthermore, the amount of the inorganic salt used to achieve a desired level of conductivity is well below those amounts which attract excessive moisture and give a limpness or raggy feeling to the sheet.

The following Examples 8 to 12 are set forth to illustrate the superior conductivity of paper that is treated With a mixture of the sulfonated polystyrene and ammonium sulfamate. In each example the paper stock is treated with 20% aqueous solution comprising about 65 weight percent of the ammonium salt of sulfonated polystyrene and 35 weight percent of ammonium sulfamate based on the total solids weight. The conductivity of the TURES OF SULFONATED POLYSTYRENE AND SUL- FAMATE SALTS Applied weight (dry basis) Megohms/ Square 1bs.l3,000

Sq. ft 44% R. H. 12% R. H.

The results in the foregoing Table II illustrate that a mixture of a salt of sulfonated polystyrene and ammonium sulfamate give paper stock with better electroconductivity than similar stock which is treated with either material used alone. Such a synergistic mixture has decided advantages over and above that of increased conductivity over a wide range of relative humidities. This synergistic combination provides a composition which utilizes the best aspect of each substance while minimizing the undesirable side effects encountered when using the inorganic salts as the sole conductive material.

The water soluble electroconductive materials of this invention may be used in combination with other materials commonly used in the paper industry without any significant loss in the conductivity of the finished paper. Furthermore, the compositions of this invention are completely compatible with clay, resinous film formers and materials commonly used in the paper industry as is illustrated by the following Example 13.

EXAMPLE 13 The paper stock hereinbefore described was treated with the following slurry to give an applied weight of hs./1000 sq. ft.

Slurry Lbs.

Ammonium salt of sulfonated polystyrene 2.0

Gelva TS-30 polyvinyl acetate emulsion (dry basis) 1.0 Clay (weight of dry solids) 1.0 Water 16.0

The ingredients were readily formulated and no incompatibility was observed in the slurry.

Paper stock treated with the above slurry gave the following conductivities.

Percent R.H. Megohms/ square 44 4.8 12 90 EXAMPLE 14 Example 13 was repeated here except that no clay was used. A dry coating weight of 2.0 lbs./ 3000 sq. ft. gave the following conductivities.

Percent R.H. Megohms/ square 44 6.0 12 870 EXAMPLE 15 This example illustrates the use of a 65/45 weight ratio of sodium salt of sulfonated polystyrene/ sodium sul- 6 fate as a water soluble electroconductive material for treating paper stock. Paper stock treated with a dry solids weight of 2 lbs/3000 sq. ft. give the following conductivities.

Percent R.H. Megohms/ square 44 4.5 12 700 The foregoing example illustrates the excellent results that are obtained when using alkali metal salts of sulfonated polystyrene and alkali sulfates in combination.

EXAMPLE 16 Example 12 is repeated here except using the ethanolamine salt of sulfonated polystyrene and sulfuric acid. Comparable results were obtained which indicates that substituted ammonium may be used as the cationic portion of the salt as well as straight ammonium.

EXAMPLE 17 Examples 1 to 6 and 8 to 12 were repeated on 55 lb. unsized kraft paper and 42 lb. sulfite bond paper. Comparable results were obtained in each instance which indicates that the water soluble electroconductive materials of this invention may be utilized with any of the well known commonly used cellulosic sheet materials.

The water soluble electroconductive materials of this invention may be introduced into the sheet material during or after the manufacture of the sheet material. In the former instance the materials of this invention may be added to the pulp or the nearly dried paper after its formation on a Fourdrinier machine. After the formation of the paper, the materials of this invention may be applied to the sheet by spraying, knife coating, roller coating, transfer rolls, etc. Also, the sheet may be brought into contact with an aqueous or methanol solution of the electroconductive materials of this invention. When the paper is to be coated with aqueous based film forming materials such as the emulsion of Examples 13 and 14, the material of this invention may be incorporated into the aqueous composition.

The sulfonated polystyrene described in the present invention may be prepared by any of the known methods such as those disclosed in the following US. Patents 2,533,210; 2,533,211 and 2,718,514. The molecular weight of these polymers is not deemed critical in this application and sulfonated polystyrene in the molecular weight of 50 to 2,000,000 are suitable for use in this invention. Preferably one would use sulfonated polystyrene having a molecular weight in the 50 to 600,000 range. For use in the practice of this invention the sulfonated polystyrene should have a degree of sulfonation of at least 0.75 units of sulfonic .acid or salts thereof per repeating styrene unit and more preferably at least 1.0 units of sulfonic acid or salts thereof per repeating styrene unit. The only critical requirement in regard to the molecular weight and the degree of sulfonation of the materials is that the molecular weight should not be so high nor the degree of sulfonation so low as to preclude the solubility of the sulfonated polystyrene and salts thereof in aqueous solution. In this regard the polymeric material should have a solubility of at least 2% by weight in aqueous solutions at 25 C.

Also contemplated in this invention is the use of the sulfonated alkyl and halogen derivatives of polystyrene such as sulfonated polymers of alpha methyl styrene, vinyl toluene, chlorostyrene, etc., wherein the alkyl and halogen groups are present as ring or side chain substituents or both.

The alkyl groups contemplated are those containing from 1 to 4 carbon atoms. In this regard the nature and number of any substituent present should be such to allow the above mentioned degree of sulfonation.

The salts of sulfuric acid and its derivatives which may be optionally used in the practice of this invention include the ammonium and alkali metal salts of sulfuric acid and sulfamic acid. As pointed out above the term ammonium includes both ammonium per se and amines which are considered substituted ammonium. Examples of suitable amines which may be used as a cationic substance include ethanol amine, morpholine, picoline, quinoline, etc. Especially useful are those hydroxy amines such as hydroxy ethyl amine and other related substances wherein the hydroxy groups increase both the solubility and the conductivity of the water soluble electroconductive materials of this invention.

This invention contemplates using from 25 to 100 Weight percent of sulfonated polystyrene and the salts thereof and conversely, from to 75% of the salts of sulfuric acid and its derivatives. Wherein in each case the weight percent given is based on the total weight of the water soluble electroconductive materials of this invention. Especially preferred are materials comprising from 50 to 95 weight percent of the polymeric material and from to 50% of the inorganic salts. Most especially preferred are compositions comprising from 50 to 90 weight percent of the polymeric material and from to 50 weight percent of the inorganic salts.

The practice of this invention contemplates using from about 0.5 to about 15.0 lbs. of Water soluble electroconductive material per 3000 sq. ft. of sheet material. Heavier coating weight may be employed but there is no apparent advantage in using these larger amounts.

The materials of this invention can also be used with those materials commonly used in the paper making industry such as pigments, opacifiers, fillers, extenders, dyes, sizes, etc.

In view of the foregoing it should be obvious that many variations can be made in this invention without departing from the spirit of this invention or the scope of the following claims.

What is claimed is:

1. Electroconductive sheet material comprising a fiber base sheet having dispersed therein from 0.5 to 15.0 lbs., per 3000 square feet of fiber base, of a water soluble conductive material comprising from to 100 weight percent, of a material selected from the group consisting of sulfonated polystyrene and salts of sulfonated polystyrene and from 0 to 75 weight percent of a salt of an acid selected from the group consisting of sulfuric acid and sulfamic acid, wherein in each case the weight percent is based on the total weight of water soluble conductive material and wherein the cation in the respective salts is selected from the group consisting of ammonium, substituted ammonium and alkali metals.

2. The electroconductive sheet material of claim 1 wherein the Water soluble conductive material is the ammonium salt of sulfonated polystyrene.

3. The electronductive sheet material of claim 1 wherein the Water soluble conductive material is the ammonium salt of sulfonated polystyrene and ammonium sulfamate.

4. The electroconductive sheet material of claim 1 wherein the water soluble conductive material is the alkali metal salts of sulfonated polystyrene and alkali sulfate.

5. A process for the preparation of electroconductive sheet material which comprises (1) treating a fiber base sheet with from 0.5 to 15.0 lbs., per 3000 square feet of fiber base sheet, of a Water soluble conductive material comprising from 25 to 100 weight percent, of a material selected from the group consisting of sulfonated polystyrene and salts of sulfonated polystyrene and from 0 to weight percent of salt of an acid selected from the group consisting of sulfuric acid and sulfamic acid, wherein in each case the weight percent is based on the total Weight of water soluble conductive material and wherein the cation in the respective salts is selected from the group consisting of ammonium, substituted ammonium and alkali metals, and (2) drying the treated sheet material.

6. The process of claim 5 wherein the sheet material is treated with an aqueous solution comprising an ammonium salt of sulfonated polystyrene and ammoninum sulfamate.

7. The process of claim 5 wherein the sheet material is treated with an aqueous solution comprising an alkali metal salt of sulfonated polystyrene and an alkali sulfate.

8. The process of claim 5 wherein the sheet material is treated during the sheet forming operation.

9. The process of claim 5 wherein the sheet material is treated after the formation of the sheet.

No references cited.

WILLIAM L. JARVIS, Primary Examiner US. Cl. X.R. 

